Various ink compositions such as solvent types, aqueous types and oil-based types have been conventionally known as inks used in inkjet printing. Among these, the demand for active energy ray-curable inkjet inks has increased in recent years due to their advantages that they can also be applied to no-absorbable substrates such as plastics and glasses, and that they decrease the volatilization volumes of solvents and thus are environment-friendly. Specifically, in the field of industrial inkjet printing, substitution of solvent type and aqueous type inkjet inks with active energy ray-curable inkjet inks is expected from the viewpoints of water resistance, dry energy of inks, adhesion of ink components to heads due to drying, and the like, besides the above-mentioned advantages.
On the other hand, in inkjet inks, the color reproducibility of an image quality formed significantly varies depending on the degrees of the color reproduction potentials that can be possessed by three colors: yellow, magenta and cyan. Therefore, selection of pigments is a very important factor.
For example, Patent Documents 1 and 2 ensure desired color regions by selecting suitable pigments, but these relate to aqueous type inkjet inks. In active energy ray-curable inkjet inks, polymerizable monomers are used as dispersion solvents. Therefore, the dispersibilities of pigments decrease, and thus it is difficult to obtain desired color regions even if similar pigments to those of Patent Documents 1 and 2 are selected.
Patent Document 3 selects a so-called solid solution in which unsubstituted quinacridone and 2,9-dichloroquinacridone are dissolved in one another in the same crystal as magenta pigment to thereby achieve a broad range of color reproduction property in an active energy ray-curable inkjet ink. However, a pigment dispersion using a solid solution is poor in storage stability. In addition, an active energy ray-curable inkjet ink using a solid solution tends to offer a slow curing velocity during printing. Therefore, use of a solid solution is considered to be not preferable in view of increasing in printing speed.
Furthermore, Patent Document 3 defines the used pigments based on transmission absorption spectra. However, the color shade and texture of a printed matter by an inkjet ink significantly depend on print media, the primary particle diameters of pigment dispersions, and the like, and thus it is considered to be preferable to evaluate a hue with consideration for a final printed matter with reflection spectra.